1. Field of the Invention
The present invention relates to an adhesive film for circuit connection, and a circuit connection structure.
2. Related Background Art
Circuit-connection films for electrically connecting mutually opposed circuit electrodes, e.g., anisotropic conductive adhesive films in which electrically conductive particles are dispersed in an epoxy type adhesive (epoxy resin base anisotropic conductive adhesive films) are commonly used for electrical connection mainly between a TCP (Tape Carrier Package) equipped with a semiconductor chip for driving a liquid crystal display (LCD; Liquid Crystal Display), and an LCD panel, or between a TCP and a printed circuit board.
In recent years, even in cases where a semiconductor chip is mounted directly on an LCD panel or on a printed circuit board by face down bonding, the flip chip packaging advantageous for thickness reduction and narrow pitch connection is adopted instead of the conventional wire bonding method, and the anisotropic conductive adhesive films are also used as circuit-connection adhesive films in this packaging.
However, the aforementioned epoxy resin base anisotropic conductive adhesive films had excellent workability but required heating at about 160-180° C. for the connection time of about 20 seconds and heating at about 180-210° C. for 10 seconds.
The reason for the need for such heating is that a catalyst curing agent inactive at ordinary temperature is used for the purpose of achieving good stability through simultaneous achievement of short-time curability (fast curability) and storage stability (shelf life) and it results in failing to achieve sufficient reaction during curing.
With recent trends toward larger scale and narrower frame of LCD modules, there arise problems of increase of thermal influence on the LCD panel and increase of warpage of the printed board in a connection operation with use of the circuit-connection adhesive film. There are also studies on replacement of the glass LCD panel substrate with a plastic one in terms of weight reduction, but the plastic materials have the problem of low thermal resistance to make mounting of the TCP difficult.
There are thus demands for low-temperature connection of the circuit-connection adhesive film as countermeasures to such problems. In addition, low-temperature fast curability is necessary and indispensable in order to meet needs for reduction of the connection time to below 10 seconds to increase production efficiency. For this reason, there are proposals of circuit-connection adhesive films with a radically polymerizable substance capable of achieving connection by heating at about 160° C. for the connection time of 10 seconds (e.g., Japanese Patent No. 3344886).